Fluid blast circuit interrupter



Feb. 26, 1957 J. w. BEATTY ET FLUID BLAST CIRCUIT vINTERRUPTIEIR 2Sheets-Sheet 1 Filed Dec. 10, 1953 Inventors:

John \N. Beattg, Hajj M. And

Feb. 26, 1957 J. w. BEATTY L FLUID BLAST cmcum INTERRUPTER 2Sheets-Sheet 2 Filed Dec. 10, 1953 Inventors: John W. Beattg, Reed M.And r50,

Their Attorney.

United States Patent FLUID BLAST CIRCUIT INTERRUPTER John W. Beatty,Lansdowne, and Reed M. Anderson, Glenolden, Pa., assignors to GeneralElectric Company, a corporation of New York Application December 10,1953, Serial No. 397,324 Claims. (Cl. 200-148) This invention relates tocircuit interrupters of the fluid-blast type and, more particularly, tomeans for controlling the blast valve and the movable contact structureof such an interrupter.

Although our invention has been illustrated by showing it as applied toan interrupter of the gas-blast type, it is to be understood that theinvention is equally applicable to interrupters of the liquid-blasttype.

In the sustained pressure type of fluid-blast circuit breaker, highspeed interruption of electrical circuits is obtained by locating therelatively movable interrupting contacts of the circuit breaker withinan interrupting chamber filled with high pressure fluid. For producing afluid-blast action which aids in extinguishing the are established whenthe contacts are separated, there is usually provided a blast valvewhich is controlled so as to cause high pressure fluid, during circuitinterruption, to flow rapidly past the contacts and to atmosphere. Inorder that a blast action be present when the contacts are separated andin order to conserve high-pressure fluid after circuit interruption, itis important that the movement of this blast valve be accuratelycoordinated with the movement of the contacts. More particularly, it ispreferred that the blast valve should open immediately prior to initialcontact separation and should close immediately after the circuit hasbeen interrupted.

It is, therefore, an object of our invention to provide a simple andreliable means for controlling the blast valve of a fluid-blast type ofcircuit interrupter.

It is a further object of our invention to interrelate the movablecontact structure and the blast valve by means of a fluid coupling whichprovides for opening of the blast valve before contact separation andwhich permits closing of the blast valve independently of movement ofthe contact structure after a predetermined contact separation.

It is a further object of our invention to incorporate a structurallysimple contact-controlling dashpot into such a fluid coupling.

It is a further object of our invention to provide a novel arrangementof relatively movable contacts which is capable of providing rapidcontact separation and is especially adapted for use in gas-blastinterrupters of the sustained pressure type.

In carrying out these objects in accordance with one form of the presentinvention, the movable contact structure and the blast valve areoperatively interconnected by a pneumatic coupling which comprises acylinder and a pair of oppositely-disposed pistons re-ciprocabletherein. One of these pistons acts as a driving piston and is coupled tothe movable contact structure, whereas the other of the pistons iscoupled to the blast valve and acts as a follower piston. Contactopening movement of the driving piston establishes on opposite sides ofthe follower piston a pressure differential acting in a direction tomove said follower piston in coupled follow-up relationship to saiddriving piston whereby to open the normally-closed 2,783,337 PatentedFeb. 26, 1957 blast valve. Means are provided for rapidly reducing thispressure differential after a predetermined opening stroke whereby torelease the follower piston so as to permit the blast valve to close.Another feature of one form of the present invention is that thecylinder has a restricted end portion which confines the gas ahead ofthe driving piston as it moves toward open position whereby to provide adashpot action at the end of the opening stroke.

Further objects and advantages of our invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize our invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of our invention, reference may be had to theaccompanying drawings in which Fig. l is an elevational view, partly insection, of a gas-blast circuit interrupter embodying the presentinvention; Fig. 2 is an enlarged sectional view taken along the line 2-2of Fig. 1; Fig. 3 is a detailed view showing a pneumatic couplingconstructed in accordance with the present invention; Fig. 4 illustratesa modified form of pneumatic coupling; and Fig. 5 illustrates stillanother modification of the pneumatic coupling of the present invention.

Referring now to Fig. 1 there is shown a circuit breaker of thegas-blast type comprising an interrupting unit generally indicated at10. This interrupting unit comprises an enclosed interrupting chamber 11defined, in part, by a metallic casing 12 and a pair of tubular members13 and 14 of insulating material mounted at opposed ends of the casing12. The interrupting chamber 11 communicates through an insulatingconduit 15 with a source (not shown) of high pressure gas so that,preferably, the chamber 11 is normally filled with gas at a pressureequal to that of the source. The outer ends of the chamber 11 are sealedby means of terminal plates 20 and 21 supported from the tubular members13 and 14. The tubular members 13 and 14, which are constructed of amaterial possessing high mechanical strength so as to be capable ofwithstanding the sustained gas pressure within chamber 11, arepreferably enclosed within tubular weather-proof porcelain insulators 22and 23. For supporting the interrupting unit 10 there is provided atubular insulating column 24 which surrounds the conduit 15 and ispreferably of porcelain.

The stationary contact structure for the circuit breaker of Fig. 1comprises, in general, a pair of elongated rod contacts 30 and 31supported from terminal plates 20 and 21, respectively, and extendinginwardly therefrom, and a centrally-disposed pair of electricallyinterconnected tubular nozzle-type contacts 32 and 33. These pairs ofcontacts define, at their extremities, a pair of gaps 25 and 26, whichare bridged by a pair of pivotally-mounted movable contact blades 34 and35. The terminal plates 20 and 21 are respectively connected to powerlines 36 and 37, so that the electrical circuit through the breaker isas follows: from power line 36 and terminal plate 20, current will flowthrough the rod contact 30, bridging contact 34, tubular contacts 32 and33, then through bridging contact 35, rod contact 31, and finallythrough the terminal plate 21 to power line 37.

For supporting the centrally-disposed tubular contacts 32 and 33 inaxially-aligned relationship, there is provided a generally cylindricalcasting 40. T he casting 49 has at its upper end a flange 41 which issupported from the casing 12 by means of a suitable flanged adaptor 42carried by the casing 12. At its lower end the casting 4b is formed witha pair of tubular projections 43 and 44 which tightly receive and areunited with the inner ends of the tubular contacts 32 and 33.

For pivotally supporting the movable bridging contacts 3d and 35, eachof the tubular projections 43 and 44 has a clevis 45 carrying a suitablepivot pin 46 extending freely through an aperture formed in the innerend of the movable bridging contact. As best seen in the sectional viewof Fig. 2, proper contact-wipe is obtained by forming the extremities ofthe rod contact 31 and the nozzle contact 33 of a rectangular externalcross-section and the bridging contact 35 with spaced arms 47havingessentially fiat inner surfaces which slidably contact the flatsides of the associated stationary contacts 31 and 33.

For effecting opening and closing operation of the bridging contacts 34and 35 of Fig. 1, there is provided a reciprocable actuating rod 50which is connected at its lower end to a suitable operating mechanism(not shown). At its upper end the actuating rod 50, which is ofinsulating materiahis connected to the pivotal bridging contacts 34 and35 throughan actuating crosshead 51 secured to the rod 53. Thiscrosshead has at each of its ends a connecting, linkSZ whichis pivotallyjoined at 54 and 53 to the vcrossheatl and a bridging contact,respectively. by suitable pivot pin structure. A compression spring 55biases the contacts 34 and 35 toward closed position. Thus, it will be.apparent that when the actuating rod 50 is moved rapidly downwardagainst the bias of spring 55, the bridging contacts 34and 35 arerapidly moved from the solid line position to the dotted line position56 whereby to effect interruption of the circuit through the circuitbreaker, as will be described in greater detail hereinafter.

For producing a gas-blast action for extinguishing the arcs which areestablished at the gaps and 26 when the bridging contacts are moveddownwardly to the dotted line position of Fig. 1, there is providedan-exhaust passage 60 which leads from the interrupting chamber 11through the tubular contacts 32, 33 and through the cylindrical castingto the surrounding atmosphere. The tubular contacts 32 and 33 areprovided with nozzle throats 57 defining inlet-s to the exhaust passage60. For controlling the flow of arc-extinguishing gas through the nozzlethroats 57 and through the exhaust passage 60, there is provided at theouter end ofv the exhaust passage 60 a cylindrically-shaped reciprocableblast. valve 61 which slides smoothly in a surrounding tubular valvehousing 62 and abuts, in its closedposition, against a stationaryannular valve seat 63. Thus, the exhaust passageway 63 is defined by thenozzle throats 57,!the inner walls. of the tubular contacts 32 and .33,the inner walls of cylindrical casting 4d, the cooperating outer wall ofa tubular valve housing-62, and the valve. seat63 which issuitablyunited to casting 4! The blast valve-61 is preferably of the balancedpiston type, as shown, and is biased toward a normally-closed positionby means of a valve reset spring 64. Since the chamber 11 is normallyfilled with high pressure gas, it will be apparent that when valve 61 ismoved downto open (by means described more fully hereinafter) gas in thechamber 11 will flow at high speed through the nozzle throats 57, andout the passage 69 past valve 61 to atmosphere. This rapid flow of gasthrough the nozzle throats 57 creates an axial arc enveloping blastaction at gaps 25 and 26 which is efliective to extinguish the Y arcsdrawn thereat.

A more specific description of the manner in which arcs are establishedand interrupted during opening operation of the breaker is as follows:When the pivoted blades 34 and 35 are moved rapidly downward, a pair ofseriesrelated arcs are established, one between rod contact and blade 34and one between rod contact 31 and blade 35. Since immediately prior tocontact separation, opening of blast valve 61 has taken place, the highpressure gas flowing into the throats 57 has created a blast action atthe gaps 25 and 26. This blast action constitutes a hose-like gas streamflowing at high speed which envelops the are so that such action rapidlytransfers. the arcs from the blades 34 and into the tubular. contacts32. and 33,

respectively, and subsequently effects rapid extinction of these'arcs.

Since any interrupting blast produces but a limited decrease in pressurein the chamber 11, high pressure gas is always present at the gaps 25and 26, and since, in general, the dielectric strength of a gas variesdirectly with its pressure, it is possible to obtain full across-thelineinsulation with only a very small contact separation at gaps 25 and 26.The small separation required makes it possible for the movable blades34 and 35 to carryout both interruption and isolation functions within avery short time after contact separation is initiated. As a result, alarge portion of the opening stroke of the blades 34 and 35 is availableand therefore is used for deceleration action without, however,affecting the interrupting or isolating characteristics of the device.For example, where each of the pivoted blades moves through a totalangle of 28 and fullinsulation is obtained after a. 14 rotation (theposition at which the space between the rod contact 34) and the blade 34approximates the space between rod contact 3% and tubular contact 323),the final 14 of rotation is available for deceleration of the movingparts of the circuitbreaker. Deceleration is further facilitated by thepivoted construction ofthe blades 34, 35, because only the outer endsofthe blades are moved at relatively high velocity. The heavier operatingmechanism is connected to the blades adjacent the pivot points dd-and,hence,,moves at a much slower speed, there-by facilitating decelerationof themoving parts at the end of the opening stroke.

Thus, from the. abovedescription of the opening characteristics of thecircuit breaker, it should be apparent that the disposition of thepivoted contact structure of the presentinven-tion within a highpressure gas chamber is a significant factor in making possible positiveinterruption and isolation within a very short tme whereby a-largeportionoof the contact opening stroke remains availableand is utilizedfor smooth deceleration of. the moving parts of. the breaker.

Itis important that movement of the blast valve 61 be accuratelycoordinated with movement of the movable contacts 32.and 33; Moreparticularly, in order to effect rapid arc extinction,- it is desirablethat thearc-extinguishing-blast action-be initiated somewhat before thearc is established between interrupting contacts. Additionally, in orderto conserve gas, it is important that the blast valve. beclosed as. soonas. the circuit has been interruptedfaftenan adequate contactseparation. For effectively. andreliably obtaining this desiredcoordinationbetween themovernent of the. blast valve 5i andthe-contacts. 34,- and.35, inv accordance with one form of thisinvention,- there is provided a pneumatic coupling 65 which operativelyinterconnects the movable contacts 34, 35 and theblast. valve 61.Referring more particularly to the detailed vie-w ofFig. 3, thepneumatic coupling 65 comprises a stationary enclosing cylinder as and apair of coaxially disposed cooperating pistonso'l' and 68-reciprocablewithinthe cylinder; The lower or driving piston 67 is actuated from .thecrossheadSl by means of a piston. rod. 69 connected between piston 67and crosshead 51'and extending slidably through a sealed opening in thelower end Wall. of the cylinder 66. The upper or follower piston 68 iscoupled to the blast valve 61 by means of a piston rod 7% which isconnected between pis ton 68' and blast valve 61., The outer peripheriesof the reciprocable pistons 6'7 and 68 are sealed with respect to theinternal wall of cylinder 65 so that substantially nogas flows past'thepistons around the outer eripheries thereof; Preferably, conventionalpiston rings (not shown) may be'used to insure a reliable seal.

The manner in which the pneumatic coupling 65 provides the desiredcoaction between the movable contacts andthe blast= valve will now 'bedescribed. When the movable contacts. are in closedposition, the piston67 and 68' are in the position of Fig. 3. Since, at its upper'end;

the cylinder 66 is provided with an inlet port 71 communicating with theinterrupter chamber 11 and since the upper piston 68 is provided with asmall bleed passage 72 extending therethrough, the gas on both sides ofthe upper piston 68 is at the same pressure as the gas at the pressuresource when the pistons are in the position of Fig. 3. The same pressurealso exists below the driven piston 67 by reason of the restricted exitport 80 from the cylinder 66 near its lower end communicating with thecasing 11. Now when the actuating rod 50 is moved rapidly downward (bymechanical means not shown) to effect opening of the circuit breaker,the lower piston 67, being directly coupled to the rod 50, also movesrapidly downward. This downward movement instantaneously reduces thepressure of the gas in the small restricted space between the twopistons whereby a pressure differential is rapidly established onaxially opposite faces of the upper piston 68. As downward movement ofthe lower piston continues, this pressure differential rapidly builds upto a value wherein it provides suflficient downward force to overcomethe opposing action of valve reset spring 64 and thereby to cause theupper piston 68 to move in follow-up relationship to the lower piston67. As a result of this movement of the upper or follower piston, theblast valve 61 is withdrawn from its seat and opened, as desired. Thesmaller the initial space between the pistons, the faster will be thefollow-up movement of the follower piston with respect to the drivingpiston. The movable contacts 34 and 35 have suflicient wipe with respectto the cooperating stationary contacts to permit the blast valve 61 tobe opened just before separation of the contacts occurs. As a result,the desired blast action has been initiated at the gaps 25 and 26 at theinstant the arcs are drawn at the gaps.

The upper piston will move downward in follow-up relationship to thelower piston until the valve 61 strikes an annular stop 75, which issupported at the top of the cylinder 66 upon an annular slightlyyieldable buffer element 76. When this abutting action occurs, downwardmovement of the upper piston 68 ceases, at an appropriate fully-openvalve position, but the lower piston 67 continues to move downward,driven by the breaker operating mechanism. This continued downwardmovement of lower piston 67 again reduces the pressure between the twopistons and, at the same time, due to the compression of gas in therestricted chamber at the underside of the piston 67, increases thepressure on the underside of pisten 67. The resulting pressuredifferential across the lower piston 67 thus produces a moderateretarding action which becomes effective during the last portion of theopening stroke. As a result, smooth deceleration of the moving parts ofthe circuit breaker is effected as the opening stroke is completed.

As previously explained, in order to conserve the high-pressure gaswithin chamber 11, the valve 61 should be returned to closed position atan appropriate point during the opening stroke, or, at least, as soon asthe opening stroke is completed. Since the circuit breaker of Fig. 1 ispreferably latched in open position by latch means (not shown), it willbe apparent that valve 61 must be capable of returning to its closedposition independently of the operating mechanism which produced openingof the valve. This independence of motion is effectively obtained in oneform of the circuit breaker of the present invention by release meanscomprising the bleed passage 72 extending through the upper piston 68.Specifically, while the contacts are moving toward fully open positionand the pistons 67 and 68 are moving downwardly in coupled follow-uprelationship, a restricted flow of gas into the space between thepistons is taking place through bleed passage 72. This flow throughbleed passage 72 tends to equalize the pressure on opposite sides of thefollower piston 68 so that after a predetermined downward movement ofthe follower piston, the pressure differential on opposite sides of thispiston is sufficiently reduced to permit valve reset spring 64 topredominate whereby to return the follower piston and the blast valve tothe closed-valve position. Preferably, the bleed passage 72 is of such asize that in approximately 3 cycles sufiicient gas flows through passage72 to effect the reversal of the follower piston and the blast valve.

From the above description of the opening operation, it will be apparentthat the pneumatic coupling 65 not only serves to effectively coordinatethe movement of the valve 61 and the contacts 34, 35 in the desiredmanner, but also serves as an efiective dashpot for smoothlydecelerating the moving parts of the circuit breaker at the end ofopening stroke.

It additionally will be apparent that the pneumatic coupling of thepresent invention is especially adapted to control the blast valve 61 ina manner which permits establishment of a blast action at the gaps 25and 26 at a very early instant after the circuit breaker responds to afault. More particularly, since the space above the valve-connectedupper piston 68 communicates freely (at 71) with the sustained-pressureinterrupter chamber 11, full supply pressure will always be presentabove the piston 68, and as a result, a large downward force on piston68, and accordingly, valve 61, is produced by a slight downward movementof the lower piston 67 from the closed position of Fig. 3. This rapidopening response of blast valve 61 permits the desired blast action tobe initiated almost simultaneously with initiation of the openingmovement of the cross head 51.

Closing operation of the breaker is effected by means of the closingspring 55 which, when unlatched, moves the crosshead 51 and the contacts34, 35 upwardly into closed position. The check valve 77 in the lowerpiston 67 permits relatively-free gas flow downwardly past piston 67thereby allowing for rapid closing operation without excessiveretardation from the pneumatic coupling 65.

Fig. 4 illustrates an alternative arrangement for obtaining the desiredindependence of motion between valve 61 and contacts 34, 35 at apredetermined point in the opening stroke. Parts in Fig. 4 whichcorrespond to the parts of Fig. 3 are designated by correspondingreference numerals. In the arrangement of Fig. 4, a release port 80a,which is relatively large compared to the port 80 of Fig. 3, is providedfor interconnecting the interrupter chamber 11 in the interior ofcylinder 66. This port 80a is preferably disposed slightly above thelowermost position 81 (shown in dotted lines) that the driving piston 67will occupy at the end of its opening stroke. As a result, when thedriving piston 67 is moved toward its lowermost position 81 with thefollower piston 68 in coupled follow-up relationship, and the port 80:!is brought into communication with the space between the pistons, thepressure ditferential on opposite sides of the upper follower pistonwill instantaneously be reduced so that the follower piston releasesfrom its driving piston to return immediately to the valve closedposition under the influence of the valve reset spring 64. It will beapparent that rapid release of the follower piston from its coupledrelationship to the driving piston may be obtained at any desired pointin the opening stroke by placing the port 80a at the desired point ofrelease along the bore of cylinder 66. It will also be apparent that byutilizing the port 80a for releasing the pistons from coupledrelationship, it is possible to dispense with the bleed passage formedin the follower piston.

In the modification of Fig. 4, a very effective retarding force isapplied to the moving parts of the breaker as the opening stroke iscompleted by virtue of the fact that as the driving piston 67 passesbelow the port 80a, the piston must compress the gas confined in theclosed lower portion of the cylinder 66.

Fig. 5 illustrates still another modification of the present inventionwherein the parts corresponding to the avssgasv parts .ofJFig. 1aredesignated by corresponding reference numerals. This modificationdiffers from those previously described, principally by reason of thefact that in Fig. 5 the actuating means for the circuit breaker isincorporated directly into the pneumatic coupling structure instead ofbeing. separate .therefrom. More particularly, Fig. 5 shows a pneumaticcoupling90 connected between the blast valve oland the crosshead 51', asin Fig. 1, but in Fig. 5 opening movement fromthe closedcontact positionshown is produced by dumpinggas from the closed cylinder below the lowerpiston 91 by means of a two-way control valve 92 controlled by suitablefault-responsive means (not shown). Sustained-pressure interruptingchamber 11 communicates freely with. the supply reservoir 88 by means ofconduit 88a, so that when the pistons are inthe contact-closed positionshown, the gas .on. both sides of lower or: driving piston 91 is at apressure corresponding to the. pressure in supply reservoir 88. This isthe casebccausethe upper side of the: piston 91 communicateszwith; thesustainedvpressure interrupting chamber 11 through an inlet 93. formedin cylinder 89 and through a bleedpassage. 94 formed in upper followerpiston 95; similarly, the lower side of driving piston 91 communicateswith the supply 38 through conduit 96 and valve 92. Accordingly, as inthe first embodiment in Fig. 3, inthe normally=closed breaker positionall pneumatic pressures above the two pistons are equalized so that theblast valve and contacts must rely upon their respective springs 64. and55 for maintaining their closing bias. Now, when control'valve 92 isrotated clockwise from the solid line position to the dotted lineposition 95:: so as to vent the conduit 96 to atmosphere, a pressuredifferential is created on opposite sides of lower piston 91. Thispressure differential is sufficient to move the piston 91andtheinterconnected crosshead rapidly downward against the bias ofclosing spring 55 and, as a result, to open the contacts of the circuitbreaker. This downward movement of the lower piston reduces the pressureon the underside of the upper piston 95 thereby causing the upper pistonto move downward in coupled follow-up relation to the lower piston untilthe valve 61 striks the stop75. The bleed passage 94 permits a meteredgas flow to the coupling space between the two pistons, so that. after apredetermined time delay, the pressures on opposite sides of the, upperpiston tend to equalize, and the valve 61 will return to closed positionunder the influence of its reset'spring 63, as described with respect tothe modification of Figs. 1-3.

An additional feature of the modification of Figure 5 is that the meansfor holding the circuit breaker in opencontact position is incorporateddirectly into the pneumatic coupling. More specifically, the lowerpiston 91 is formed with an annular raised seat 97 which seats insealing relation against the lower wall 98 of. cylinder 89 when thepiston 91 is in its lowermost position. When this condition occurs, theforce exerted by the gas pressure above the lower piston 91 maintainsthe piston in.

its lowermost position so long as the control valve 92 is open toatmosphere. This provides a simple and effective means for holding thecircuit breaker contacts in open position, as desired.

Closing operation of the circuit breaker of Fig.5 may be effected byreturning control valve 92 from venting position 95a to the solid lineposition, thereby supplying high pressure gas to the underside of lowerpiston 91. This high pressure gas acting together with the'spring 55moves the piston 91 upwardly, whereby to close the contacts of thecircuit breaker. The check .valve 99 disposed in upper piston, 95permits the lower piston 91 to move upwardly without appreciableretardation resulting from the air in the coupling space ahead of theupwardly moving piston 91.

While we have shown and describedparticular-embodimentsiof ourinvention, it will be obvious to those:

skilled inrthe art'that various changes and modifications may be madewithout departing, from our invention in its broader aspects and, we,therefore, aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A fluid-blast circuit interrupter comprising separable contacts, ablast valve movable to control the flow of fluid adjacent said contacts,an actuating member movable to separate said contacts, fluid couplincylinder structure, a follower piston movable in said cylinder structureand coupled to said blast valve, and means comprising a driving pistondisposed in said cylinder structure and movable with said actuatingmember to establish on opposite faces of said follower piston a pressuredifferential acting in a direction to move said follower piston incoupled follow-up relationship to said driving piston.

2. A fluid-blast circuit interrupter comprising separable contacts, ablast valve movable to control the flow of fluid adjacent said contacts,an actuating member movable to separate said contacts, a fluid couplingoperatively interconnecting said blast-valve and said actuating member,said fluid coupling comprising a follower piston operativelyconnected-to said blast valve and means comprising a driving pistonmovable with said actuating member to establish on opposite sides ofsaid follower piston a pressure differential acting in a directiontoward said follower piston whereby to move said follower piston incoupled follow-up relation to said driving piston.

3. A fluid-blast circuit interrupter comprising separable contacts, ablast valve movable to control the flow of fluid adjacent said contacts,an actuating member movable to effect separation of said contacts, fiuidcou pling cylinder structure, a follower piston movable in said cylinderstructure and coupled to said blast valve, a driving piston disposed insaid cylinder structure and movable with said actuating member through apredetermined stroke, said cylinder structure having an essentiallyclosed wall portion slidably and sealingly receiving said pistons torestrict entry of fluid into the space between said pistons during atleast a portion of said stroke thereby to couple said pistons to movesubstantially together during said portion of the stroke.

4. A fluid-blast circuit interrupter comprising separable contacts, ablast valve movable to control the flow of fluid adjacent said contacts,an actuating member movable to effect separation of said contacts, fluidcoupling cylinder structure, a follower piston movable in said cylinderstructure and coupled to said blast valve so as to occupy a firstpredetermined position when said valve is closed, a driving pistondisposed in said cylinder structure and coupled to said actuating memberso as to occupy a second predetermined position when said contacts areclosed, Lsaid cylinder structure having an essentially closed wallportion which extends between said predetermined positions of saidpistons and sealingly receives said pistons so as to restrict the flowof fluid into the space between said pistons whereby movement of saiddriving piston away from said follower piston reduces the fluid pressurein the space between said pistons whereby to move said follower pistonin coupled follow-up relationship to said driving piston.

5. A fluid-blast circuit interrupter comprising relatively movablecontacts, an actuating member for moving one of said contacts through anopening stroke between a closed and a fully-open position, a biasedclosed blast valve openable to provide a flow of fluid adjacent saidcontacts during said opening stroke, fluid coupling comprising afollower piston operatively connected to said blast valve and meanscomprising a driving piston movable with said actuating member forestablishing on opposite sides of said follower piston a pressuredifferential acting in a direction to movesaid-followerpiston infollow-up relation to said driving piston during said opening strokethereby to open said blast valve during said opening stroke, and releasemeans eifective after a predetermined portion of said opening stroke forreducing said pressure differential whereby to permit said biased closedblast valve to return to its closed position.

6. A fluid-blast circuit interrupter comprising relatively movablecontacts, an actuating member for moving one of said contacts through anopening stroke between a closed and a fully-open position, a biasedclosed blast valve openable to provide a flow of fluid adjacent saidcontacts during said opening stroke, a fluid coupling comprising afollower piston operatively connected to said blast valve and meanscomprising a driving piston movable with said actuating member toestablish on opposite sides of said follower piston a pressuredifferential acting in a direction to cause said follower piston to movein follow-up relation to said driving piston during said opening strokethereby to open said blast valve during said opening stroke, saidpistons defining a space therebetween after movement through apredetermined portion of said opening stroke, release means comprising apassageway communicating with said space and with a source of fluid at ahigher pressure than the fluid in said space whereby to admit relativelyhigh pressure fluid to said space so as to reduce said pressuredifferential sutficiently to permit said biased closed blast valve toreturn to closed position.

7. The interrupter of claim 6 in which said passageway is a bleedpassage formed in said follower piston.

8. A fluid-blast circuit interrupter comprising relatively movablecontacts, an actuating member for moving one of said contacts through anopening stroke between a closed and a fully-open position, a biasedclosed blast valve openable to provide a flow of fluid adjacent saidcontacts during said opening stroke, a fluid coupling arranged to effectopening of said blast valve during said opening stroke, said couplingcomprising cylinder structure, a follower piston disposed in saidcylinder structure and coupled to said blast valve, and means comprisinga driving piston disposed in said cylinder structure and movable withsaid actuating member to establish on opposite sides of said followerpiston a pressure differential acting in a direction to cause saidfollower piston to move in followup relationship to said driving pistonduring said opening stroke, said pistons defining a space therebetweenafter movement through a predetermined portion of said opening stroke,release means comprising a passageway formed in said cylinder structureand communicating with said space and with a source of fluid at apressure higher than the fluid pressure in said space whereby to admitrelatively high pressure fluid to said space so as to reduce saidpressure differential sufliciently to permit said biased closed blastvalve to return to closed position.

9. A fluid-blast circuit interrupter comprising separable contacts, ablast valve movable to control the flow of fluid adjacent said contacts,an actuating member movable to effect separation of said contacts, afluid coupling operatively interconnecting said blast valve and saidactuating member, said fluid coupling comprising cylinder structure, afollower piston disposed in said cylinder structure and operativelyconnected to said blast valve and means comprising a driving pistonmovable with said actuating member to establish on opposite sides ofsaid follower piston a pressure differential acting in a direction tocause said driven piston to move in follow-up relation to said drivingpiston, said driving piston being movable between a first positionwherein the contacts are closed and a second position wherein thecontacts are fully-open, said cylinder structure having adjacent saidsecond position a restricted end portion cooperating with said drivingpiston to retard said driving piston as it moves into said secondposition.

10. A fluid-blast circuit interrupter comprising rela' tively movablecontacts, a blast valve movable to control the flow of fluid adjacentsaid contacts, an actuating member for effecting relative movement ofsaid contacts, a

fluid coupling comprising cylinder structure, a driving piston movablein said cylinder structure and operatively connected to said actuatingmember and a follower piston movable in said cylinder structure andoperatively conneoted to said blast valve, said driving piston beingmovable through a predetermined stroke corresponding to relativemovement of the contacts from a closed to a fullyopen position, pressurecontrol means for causing said follower piston to move in follow-uprelationship to said driving piston, and stop means limiting themovement of said follower piston to a stroke which is shorter than saidpredetermined stroke for said driving piston.

ll. A fluid-blast circuit interrupter comprising relatively movablecontacts, a blast valve movable to control the flow of fluid adjacentsaid contacts, an actuating member for effecting relative movement ofsaid contacts, a fluid coupling comprising cylinder structure and adriving and a follower piston movable therein, said driving piston beingmovable with said actuating member and said follower piston beingoperatively connected to said blast valve, said driving piston beingmovable through a predetermined stroke corresponding to relativemovement of the contacts from a closed to a fully-open position,pressure control means for causing said follower piston to move infollow-up relationship to said driving piston, stop means limiting themovement of said follower piston to a stroke which is shorter than saidpredetermined stroke for said driving piston, said cylinder structurehaving a restricted end portion adjacent the position which said drivingpiston occupies when said contacts are in fullyopen position.

' 12. A fluid-blast circuit interrupter comprising a chamber filled withfluid under pressure, separable contact members mounted Within saidchamber, an actuating members movable to separate said contact member,an exhaust passage extending from said chamber to a region of lowerpressure, a blast valve movable to control the fluid flow through saidexhaust passage, cylinder structure, a follower piston having oppositelydisposed faces and movable in said cylinder structure, said followerpiston being coupled to said blast valve, a driving piston disposed insaid cylinder structure and cooperating with one face of said followerpiston to define between said pistons a coupling space containing fluidat a predetermined pressure, the other face of said follower pistonbeing in free communication with said chambr, said driving piston beingmovable with said actuating member to reduce the fluid pressure in saidcoupling space whereby to move said follower piston in coupled follow-uprelationship to said driving piston.

13. In a fluid-blast circuit interrupter, a stationary nozzle-typecontact of tubular configuration, a second contact disposed in generallyaxially-aligned relationship with said tubular contact and spacedtherefrom to define a gap between said contacts, a cooperating movablecontact member mounted for pivotal movement toward and away from saidgap, said movable contact member having a bridging portion which bridgessaid gap when the contact member has been moved toward said gap andwhich is spaced from said gap when the contact member has been movedaway from said gap, means including an actuating member connected tosaid contact member for producing pivotal movement of said contactmember toward and away from said gap, and means operable upon movementof said contact member away from said gap to produce a fluid blast whichflows through said gap and then into said nozzle type tubular contact.

14. A circuit interrupter comprising a plurality of generallyaxially-aligned pairs of stationary contacts defining a pair of gaps, apair of cooperating movable contact members each having a bridgingportion which bridges one of said gaps, each of said movable contactmembers being pivotally mounted on pivot structure, actuating mechanismfor producing simultaneous movement of said movable contacts, saidactuating mechanism comprising a reciprocable c'ross-headimemberwhichis. connected to. each of. said movable contact membersat atpointon. the movable contactv memberilocated between. said pivot structureandsaid bridgingiportion.

15. A fluid-blast circuit interrupter comprising separable contacts, ablast valve-movableto control the flow of fluid. adjacent said.contacts, an actuating. member movable to separate saidcontacts, and afluid coupling comprising cylinder-structure and a pair of relativelymovable pistons reciprocable in said cylinder structure, one of saidpistons being operatively connected to said blast valve and the-other ofsaid pistons being operatively connected to said actuating member,flowcontrol means for exhausting the space at one. side of said otherpiston to a region, of lowerpressure whereby said other piston acts as.thedriving means for-said actuating member.

16. Afluid-blast. circuitinterrupter comprising separable contacts, a.blastsvalve movable tocontrol the flow of fluid adjacent said'contacts,anactuating member movable to separatesaid contacts, a fluid couplingcontaining fluid under pressure and operativelyinterconnectingsaid blastvalve and said actuating member, said coupling comprisingafollowerpiston operatively connected to said blast valve and meanscomprising a driving piston movable with saidactuatingmember toestablish a pressure diflerential. on opposite sides of said drivenpiston. so as to cause,saidfollowerpiston to move in follow-up relationto said driving piston, flow control. means for exhausting the space atone side of said driving piston to a region lower pressure whereby said"driving piston acts as the driving means for said actuating member.

17. A fluid-blast circuit interrupter comprising separable contacts, ablast valve movable .to control the flow of fluid adjacent saidcontacts, an actuating member movable to separate said contacts, a fluidcoupling containing fluid under pressure and operatively interconnectingsaid blast valve and said operating mechanism, said fluid couplingcomprising a follower piston operatively connected to said blast valveand means comprising a driving piston movable with said actuating memberto establish a pressure differential on opposite sides of said followerpiston acting in a direction to cause said follower piston to move infollow-up relation to said driving piston, flow control means forproducing a reduced pressure on one side of said driving piston wherebysaid driving piston acts as-the driving means for said actuating member,means for maintainingsaid reduced pressure on said" one isideiofz. said.id'riving piston: when said. contacts are: fully-open whereby 'to hol'd.said contacts in .fullyopen position;

'18.. The interrupter of claim 17 in which said flow control meanscomprises'a passageextending from said cylinder, and said driving pistonhavingra portion which seals ofi said passage when the drivingpiston ismoved to a position corresponding to the fully-open contact positionwhereby the contacts are-held infully-open position by fluid pressurewithin said cylinder.

19. In a fluid-blast circuit interrupter, separable contacts, a blastvalve movable to an open position to produce a flow of fluid adjacentsaidcontacts, cylinder structure, a'first piston movable Within saidcylinder structure and coupled to said blast valve; a secondpistonmovable within said cylinder-structure and coupled in motiontransmittingrelationwith one of-said-contacts, and means for establishing onopposite-sides of each ofsaid pistons a pressure differential which.drives said first piston. in

a direction to opensaid valve andudrives said second.

piston. in a directiontoseparatesaid contacts, and means responsive tomovement of saidsecondpiston for equalizing the pressure on oppositesides of said first piston to allow saidvalve to close.

20. In a fluid blast. circuit interrupter, separable contacts, anormally-closed blast valve movable to an open position toproduce a flowof Ifluid adjacent said con-. tacts, cylinder structure, a first pistoncoupled to said blast valve and" movable within said 'cylinder structureinone direction to open said blast valve, a second piston coupled to oneof said contacts and movable Within said cylinder structure in the samedirection as said first piston during opening of said contacts, meansfor releasably coupling said pistons together for movement in the samedirection duringa contact-opening operation, and means responsive tomovement'of said contact-coupled piston in said one direction to admitpressurized fluid into a space betweensaid two'pistons whereby'torelease the coupling between said pistons andthus allow the valve toclose.

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